Abstract:

A torsional vibration damper comprises an outer housing, an inner part
that is concentric relative to the outer housing, a plurality of chambers
formed between the outer housing and the inner part, which are filled
with a damping medium and are connected to one another through overflow
channels, and a plurality of leaf spring assemblies that are arranged in
the chambers and join the outer housing and the inner part with one
another in a torsionally flexible manner. The leaf spring assemblies have
machining-induced deflections. Two leaf springs with substantially
similar deflections are each arranged within a chamber. The leaf spring
pairs may be arranged in a mirror-image array or in parallel to one
another. Thus, the manufacturing cost of a torsional vibration damper can
be reduced, while its compact outer dimensions can be maintained.

Claims:

1. A torsional vibration damper, comprising:an outer housing,an inner part
that is concentric relative to the outer housing,a plurality of chambers
formed between the outer housing and the inner part, which are filled
with a damping medium and are connected to one another through overflow
channels, anda plurality of leaf spring assemblies, each having one or
more leaf springs, which are arranged in the chambers and join the outer
housing and the inner part in a torsionally flexible manner,wherein the
leaf springs of the leaf spring assemblies have machining-induced
deflections and pairs of two leaf spring assemblies with substantially
identical deflections are each arranged in one chamber.

2. The torsional vibration damper according to claim 1, wherein least one
groove is formed on the inner part along a circumferential direction of
the inner part and that two leaf spring assemblies having substantially
similar deflections are arranged inversely and are supported by the same
groove in circumferential direction.

3. The torsional vibration damper according to claim 2, further comprising
first grooves having a first width for supporting pairs of first leaf
spring assemblies and second grooves having a second width for supporting
pairs of second leaf spring assemblies.

4. The torsional vibration damper according to claim 3, wherein the leaf
spring assemblies of the first pairs of leaf spring assemblies have
deflections being directed away from each other in the direction of their
inner part ends and the leaf spring assemblies of the second pairs of
leaf spring assemblies have deflections directed towards each other in a
direction of their inner part ends.

5. The torsional vibration damper according to claim 1, wherein the leaf
springs assemblies have deflections in the same direction with
substantially identical dimensions and that pairs of leaf spring
assemblies are spaced apart on their outer housing ends by one or more
inserts.

6. The torsional vibration damper according to claim 1, wherein the leaf
spring assemblies include first leaf spring assemblies and second leaf
spring assemblies, wherein in first pairs of first leaf spring assemblies
the leaf springs have deflections away from each other in the direction
of their inner part ends and in second pairs of second leaf spring
assemblies the leaf spring assemblies have deflections towards each other
in a direction of their inner part ends.

7. The torsional vibration damper according to claim 1, wherein the leaf
springs have deflections towards the same direction with substantially
similar dimensions and that leaf spring pairs are spaced apart on their
outer housing ends by one or more inserts.

8. The torsional vibration damper according to claim 1, whereina plurality
of grooves is formed on the inner part along a circumferential direction
of the inner part,the leaf spring assemblies include first leaf spring
assemblies and second leaf spring assemblies, wherein in first pairs of
first leaf spring assemblies the leaf springs have deflections away from
each other in the direction of their inner part ends and in second pairs
of second leaf spring assemblies the leaf spring assemblies have
deflections towards each other in a direction of their inner part ends,
and thatthe leaf spring assemblies in a pair of two leaf spring
assemblies have substantially similar deflections, are arranged inversely
and are supported by the same groove in circumferential direction.

9. The torsional vibration damper according to claim 8, wherein the leaf
springs have deflections towards the same direction with substantially
identical dimensions and that leaf spring assemblies at least of second
pairs of leaf spring assemblies are spaced apart on their outer housing
ends by one or more inserts.

10. A torsional vibration damper, comprising:an outer housing,an inner
part that is concentric relative to the outer housing,a plurality of
chambers formed between the outer housing and the inner part, which are
filled with a damping medium and are connected to one another through
overflow channels, anda plurality of leaf spring assemblies, each having
at least one leaf spring, which are arranged in the chambers and join the
outer housing and the inner part in a torsionally flexible manner,wherein
the leaf springs of the leaf spring assemblies have machining-induced
deflections and pairs of two leaf spring assemblies with substantially
identical deflections are each arranged in parallel to one another within
one chamber.

11. The torsional vibration damper according to claim 10, wherein at least
one groove is formed on the inner part along a circumferential direction
of the inner part and that the leaf spring assemblies of a pair of leaf
spring assemblies are supported by the same groove in circumferential
direction.

12. The torsional vibration damper according to claim 11, wherein all
grooves on the inner part have the same groove width.

13. The torsional vibration damper according to claim 10, wherein all leaf
springs have equidirectional deflections.

14. The torsional vibration damper according to claim 10, wherein the leaf
spring assemblies of at least one pair of leaf spring assemblies are
spaced apart on their outer housing ends by one or more inserts.

15. The torsional vibration damper according to claim 10, wherein a
plurality of grooves is formed on the inner part along a circumferential
direction of the inner part and that the pairs of leaf spring assemblies
are supported in circumferential direction by the grooves, respectively,
and all leaf springs have equidirectional deflections.

16. The torsional vibration damper according to claim 15, wherein the leaf
spring assemblies of at least one pair of leaf spring assemblies are
spaced apart on their outer housing ends by one or more inserts.

17. The torsional vibration damper according to claim 10, whereina
plurality of grooves is formed on the inner part along a circumferential
direction of the inner part and that the pairs of leaf spring assemblies
are supported in circumferential direction by the grooves,
respectively,all leaf springs have equidirectional deflections, andall
grooves on the inner part have the same groove width.

Description:

[0002]The present invention relates to a torsional vibration damper,
comprising an outer housing, an inner part that is concentric relative to
the outer housing, a plurality of chambers formed between the outer
housing and the inner part, which are filled with a damping medium and
are connected to one another through overflow channels, and a plurality
of leaf spring assemblies that are arranged in the chambers and join the
outer housing and the inner part with one another in a torsionally
flexible manner.

[0003]Torque transmission between the inner part and the outer housing is
carried out flexibly by means of the leaf spring assemblies. With a
relative rotation between the inner part and the outer housing, the
displacement of the damping medium between the outer housing and the
inner part causes a damping effect.

[0004]Such torsional vibration dampers are used primarily in large
two-stroke and four-stroke diesel engines and gas engines for
counteracting the torsional vibrations in the power train. The torsional
vibration damper, whose outer diameter can be up to three meters, is, for
example, flanged to the crankshaft of the engine. However, torsional
vibration dampers of the type mentioned above can also be used on other
rotating parts such as camshafts, intermediate shafts and axle drive
shafts, as well as gearboxes. Such torsional vibration dampers are known
from U.S. Pat. No. 3,996,767 A and U.S. Pat. No. 6,238,294 B1.

[0005]In practice, the production of the leaf spring assemblies is
difficult as their flexural behavior must be adapted to the desired
purpose of application. Typically, this requires machining in order to
produce a wedge-shaped tapering of the leaf springs towards the inner
part, as described in U.S. Pat. No. 6,238,294 B1. Due to material
properties, such machining causes a distortion of the component, which
after removal from its set-up fixture emerges in the form of a
deflection. This deflection is difficult to predict and must be removed
with considerable effort, as the use of deformed leaf springs would
adversely affect the characteristic curve especially around the initial
position of the damper under no-load conditions.

[0006]The machining-induced deflections of the leaf springs can be
explained in the following. Spring steel, the type of steel used for leaf
springs, is produced in a rolling process and is straightened afterwards.
The rolling process causes compressive stress within the spring steel. In
the straightening process this compressive stress is superposed with
compressive and/or tensile stresses. After manufacturing a wedge-like
tapering of the leaf springs through machining internal stresses are
released causing the leaf springs to distort into unpredictable
directions depending on the previously effected straightening. This
manufacturing-induced distortion has led to a high rate of rejection.

[0007]Against this drawback the present invention aims at reducing the
manufacturing cost and effort of the above mentioned torsional vibration
damper while maintaining compact outer dimensions.

[0008]In order to overcome the shortcomings inherent to the prior art the
present invention provides a torsional vibration damper, comprising an
outer housing, an inner part that is concentric relative to the outer
housing, a plurality of chambers formed between the outer housing and the
inner part, which are filled with a damping medium and are connected to
one another through overflow channels, and a plurality of leaf spring
assemblies, each having one or more leaf springs, which are arranged in
the chambers and join the outer housing and the inner part in a
torsionally flexible manner, wherein the leaf springs of the leaf spring
assemblies have machining-induced deflections and pairs of two leaf
spring assemblies with substantially identical deflections are each
arranged in one chamber.

[0009]In a surprisingly simple manner the present invention enables the
use of leaf springs having distortions in the form of machining-induced
deflections. The costly and time-consuming straightening of the leaf
springs is thus no longer necessary. Moreover, even leaf springs, which
would be waste material in a conventional design, can be used.

[0010]Thus, the manufacturing process can be simplified significantly
without affecting the functionality of the damper. According to the
present invention, machining-induced distortion of the leaf springs is
allowed, which can be different for each leaf spring. However, the leaf
springs are arranged in such a manner that distortion only becomes
obvious in a static torsion of the outer part relative to the inner part.
This static torsion does not affect the functionality of the torsional
vibration damper. According to the invention, the only relevant property,
the mean prestress of all spring pairs to be maintained, can be
maintained in this simple manner.

[0011]In an advantageous embodiment leaf spring assemblies with similar
deflections create a greater pre-stress when arranged in a mirror-image
array within the first chambers, while an opposing mirror-image
arrangement of leaf springs within adjacent secondary chambers creates a
minor prestress of the leaf springs. Regarding the damper as a whole, the
different prestresses of the leaf springs counterbalance each other to
one dimension, as opposed to merely an arrangement of leaf springs
without deflections. This results in a very homogenous behavior of the
damper flexibility depending on the relative rotation between the inner
part and the outer housing.

[0012]According to an advantageous embodiment of the invention two leaf
spring assemblies having substantially identical deflections are
supported by a groove formed on the inner part along a circumferential
direction of the inner part.

[0013]Preferably, the leaf spring assemblies are spaced apart from each
other up to their contact edges on the outer housing, so that they are
able to deflect without making contact with each other.

[0014]Initially, the leaf springs of the leaf springs can be machined in a
simple conventional manner by means of the removal of material. By
subsequent measuring of the deflection, appropriate groups of leaf spring
with commensurate and equidirectional deflections can be formed. The
selected groups of leaf springs can then be assembled afterwards into a
damper.

[0015]The above mentioned object is accomplished further with a torsional
vibration damper comprising an outer housing, an inner part that is
concentric relative to the outer housing, a plurality of chambers formed
between the outer housing and the inner part, which are filled with a
damping medium and are connected to one another through overflow
channels, and a plurality of leaf spring assemblies, each having at least
one leaf spring, which are arranged in the chambers and join the outer
housing and the inner part in a torsionally flexible manner, wherein the
leaf springs of the leaf spring assemblies have machining-induced
deflections and pairs of two leaf spring assemblies with substantially
identical deflections are each arranged in parallel to one another within
one chamber.

[0016]As in the solution suggested above leaf springs with
machining-induced deflections are used here as well. By arranging leaf
springs with substantially identical deflections in parallel, an
uncontrolled prestress within the leaf spring pairs is avoided and thus a
continuous behavior of the flexibility of the damper around an initial
position of the damper under no-load conditions is assured. There is a
certain displacement of the rotational angle according to the deflections
between the fixations of the leaf springs on the outer housing and the
inner part. However, this does not in any way affect the characteristic
curve of the damper.

[0017]Further advantageous embodiments are indicated in the claims.

[0018]In an advantageous embodiment, two leaf spring assemblies having
substantially identical deflections are supported by a groove formed on
the inner part along a circumferential direction of the inner part. This
enables repeated loads on the springs and thus a better utilization of
material in comparison to alternating loads. In cases where the required
displacement of the single leaf springs is very high, one or more spacers
between the springs of a leaf spring pair may extend the way of the tips
of the leaf springs.

[0019]By individually modifying the support on the outer housing and/or
the inner part it is possible to ensure that in a damper under no-load
conditions all leaf springs of the damper are similarly loaded, i.e. that
they have the same prestress or that at least they bear against a flank
of the groove with zero-clearance.

[0020]The following detailed description of the present invention will be
given with the help of the exemplary embodiments shown in the
accompanying drawing. The drawing illustrates in:

[0021]FIG. 1 a schematic longitudinal sectional view of a torsional
vibration damper according to a first exemplary embodiment,

[0022]FIG. 2 a sectional view of the torsional vibration damper of FIG. 1,
and in

[0024]FIGS. 1 and 2 show a torsional vibration damper 10, which can be
coupled to a rotating component 20, such as a crankshaft. The torsional
vibration damper 10 includes an outer housing 11 extending along the
longitudinal axis A as well as an inner part 12 that is concentric
relative to the outer housing 11. The outer housing 11 and the inner part
12 delimit a plurality of separate chambers 13, which are filled with a
damping medium, such as pressurized oil. The chambers 13 are arranged in
sequence in a circumferential direction and connected to one another
through overflow channels 14. The overflow channels 14 are formed by gaps
between the inner circumferential sections of the outer housing 11 and
the outer circumferential sections of the inner part 12. In the chambers
13, there are torque-transmitting leaf spring assemblies 15, which join
the outer housing 11 and the inner part 12 in a torsionally flexible
manner, so that the outer housing 11 can be rotated in a certain angular
range relative to the inner part 12. With such a relative rotation, a
deformation of the leaf spring assemblies 15 and a displacement of the
damping medium through the overflow channels 14 can occur, resulting in a
damping effect.

[0025]The leaf spring assemblies 15 are shown more detailed in FIG. 2.
Each leaf spring assembly 15 comprises two leaf springs 16 and 17 made
out of spring steel, that are fixed to the outer housing 11 on an end
portion. In the exemplary embodiment shown, the leaf springs 16 and 17
are held between intermediate pieces 18 which separate the chambers 13
and are fixed by means of a tightening ring 19. The leaf springs 16 and
17 each extend with their free ends towards a groove 20 formed on the
outer circumference of the inner part 12, which forms two opposing flanks
in a circumferential direction. In the middle position in a damper under
no load conditions shown in FIG. 2, the leaf springs 16 and 17 are held
each against one of the flanks of the groove 20 with a defined
prestressing force. In any case, in the middle position the leaf springs
16 and 17 bear against one of the flanks of the groove with
zero-clearance. Between the free ends of the leaf springs 16 and 17, a
free space 21 is left in order for the leaf springs 16 and 17 to be able
to deflect in a non-contacting way.

[0026]The leaf springs 16 and 17 each show a machining-induced deflection
leading to a heightened or reduced prestress of the spring pair 16, 17
within the groove 20 as compared to leaf springs without distortions or
deflections. These deflections inevitably result from the manufacturing
process of the spring steel and the subsequent machining of the leaf
springs 16 and 17 by the removal of material. According to the invention,
two leaf springs 16 and 17 with substantially equidirectional deflections
are each arranged in a mirror-image array within a chamber 13. In the
exemplary embodiment shown, each of the leaf springs 16 and 17 of a leaf
spring pair has a machined wedge-shaped surface 22 or 23, so that the
leaf springs 16 and 17 taper from their respective contact edges 24 as
well as the corresponding contact edges 25 and 26 on the outer housing 11
or the intermediate pieces 18 towards the inner part 12. Here, the
wedge-shaped surfaces 22 and 23 are directed towards each other. The leaf
springs 16 and 17 may also be implemented as double wedge types.

[0027]The leaf springs 16 and 17 of first leaf spring pairs show
deflections being directed away from each other in the direction of the
inner part 12. FIG. 2 further shows second leaf spring pairs with leaf
springs 16' and 17' having deflections directed towards each other in a
direction of their inner part ends and being arranged alternately to the
first leaf spring pairs 16, 17, so that in a damper 10 there is the same
number of first and second leaf spring pairs 16, 17 and 16', 17'. In the
second leaf spring pairs 16', 17' the wedge-shaped surfaces 22' and 23'
are located on sides directed away from each other. In order keep the
free ends of the leaf springs 16' and 17' from contacting each other due
to the deflection and from rubbing against each other during operation,
the outer housing ends of the leaf springs 16' and 17' are spaced apart
by one or more inserts 27. In principle, corresponding inserts 27 may
also be provided between the leaf springs 16 and 17 of the first leaf
spring pairs.

[0028]Due to their manufacturing-induced deflections, the leaf springs 16
and 17 or 16' and 17', respectively, cause greater or lower prestresses
within the grooves 20 and 20'. Leaf springs with similar deflections
create a greater prestress, for example, by arranging the leaf springs 16
and 17 in a mirror-image array within one chamber, whereas an opposing
mirror-image arrangement within the adjacent chamber creates a minor
prestress of the leaf springs 16', 17'. Regarding the damper as a whole,
the different prestresses of the leaf springs counterbalance each other
to the same dimension, as opposed to an arrangement with leaf springs
without deflections. This results in a very homogenous behavior of the
flexibilities of the damper depending on the relative rotation between
the inner part and the outer housing. Straightening of the leaf springs
16 and 17 or 16' and 17', respectively, is not required.

[0029]In FIG. 3, three additional exemplary embodiments of a torsional
vibration damper are shown, which has the same structure as the torsional
vibration damper of the first exemplary embodiment with regard to the
outer housing 111, the inner part 112, the chambers 113 and the overflow
channels 114 as well as the functionality of the leaf spring assemblies.
Here too, leaf springs 116 and 117 or 216 and 217, respectively, out of
spring steel are used, having machining-induced deflections. However, in
this additional exemplary embodiment two leaf springs 116 and 117 and 216
and 217, respectively, with substantially the same deflection are each
arranged in parallel within a chamber 113, with their equidirectional
deflection tendencies not creating an increase or reduction of the
desired prestress of the spring pairs within the grooves 120 and 220.

[0030]In the exemplary embodiment shown in FIG. 3--center, two leaf
springs 116 and 117 are supported by a groove 120 formed in an inner part
112 in a circumferential direction of the inner part 112. The leaf
springs 116 and 117 are fixed on the outer housing 111 by means of a
tightening ring 119 and taper towards the inner part 112. Here, the
machined wedge-shaped surfaces 122 and 123 face towards the same
direction. All grooves 120 on the inner part 112 have the same groove
width. Moreover, the receiving parts on the outer housing 111 for all
leaf spring assemblies are of the same type. In order to allow for all
leaf springs 116 or 117 to be stressed in the best possible way, the leaf
springs 116 and 117 are optimized and correspondingly machined referring
to the dimensions shown in FIG. 3--center, that is the width u of the
leaf springs on their outer housing ends and the width t of the leaf
springs on their inner part ends. Here, the fixing surfaces of each leaf
spring 116 and 117 on the outer housing 111 with a fixing length e are
parallel to each other, resulting in low production costs and minimal
usage of material for the single leaf springs 116 and 117.

[0031]In a variation of the exemplary embodiment shown in FIG. 3--center,
it is possible to further influence the distance of the outer housing
ends of the leaf springs by the arrangement of inserts 127 (FIG.
3--right-hand). Moreover, by means of the fixing length e of the leaf
springs 116 and 117 on the outer housing 111, the optimal utilization of
the springs can be adjusted. Preferably, the fixing length e is the same
for all leaf spring assemblies on the damper and the width of the insert
127 is chosen thus, that the leaf springs 116 and 117 will not contact
each other within the groove 120 during their deflection. This results in
a repeated load on the springs and thus in a better utilization of the
spring tension of the damper.

[0032]In an additional embodiment (FIG. 3--left-hand), the parameters u
and t as well as the free distance s between the inner part ends of the
leaf springs are optimized such that on the one hand the best possible
tensional utilization of the springs 216, 217 is achieved, and also the
width of the groove 220, s+2×t is adjusted to the smallest possible
size. Thus, a space-optimized design is achieved in which a maximum
number of leaf springs 216 and 217 can be housed in a damper 10, as well
as a maximum moment of inertia of the outer housing 111 per volume use
can be reached. However, the production of the components thus becomes
more costly, as usually the fixing of the springs on the outer part 111
is no longer parallel resulting in an increased use of material.

[0033]The present invention has been disclosed with the help of detailed
descriptions of advantageous exemplary embodiments. It is, however, not
limited hereupon but comprises all embodiments defined in the
accompanying claims.